Snap acting switch assembly



Sttpt. 9, 1969 J c, RECHQU ET AL 3,466,587

SNAP ACTING SWITCH ASSEMBLY m e e M "V m 4 i m y 8/ 2 m v r 5 4/ E B WY 1 O m; m 6 D Filed April 28. 1967 INVENTORS JACQUES c. RECHOU JOHN L. SLONNEGER %%M ATTORNEY United States Patent 3,466,587 SNAP ACTING SWITCH ASSEMBLY Jacques C. Rechou, La Celle-Saint-Cloud, France, and John L. Slonneger, Morrison, Ill., assignors to General Electric Company, a corporation of New York Filed Apr. 28, 1967, Ser. No. 634,646 Int. Cl. H01h 37/12, 37/54, 37/74 US. Cl. 337-347 9 Claims ABSTRACT OF THE DISCLOSURE Thermally responsive low energy bimetallic actuating switch unit has low force and temperature differential characteristics, as well as a consistently eflicient contact weld-breaking motion, especially desirable for such applications as controlling air conditioning and refrigeration apparatus. A switch blade element and a toggle spring are securely fastened to a support member and a selectively actuable push rod member is biased against the blade member by a bimetallic member intermediate the ends of the blade and bimetallic members. Movement of the bimetallic member intermediate its ends operates the blade element through the push rod against the force exerted on it by the toggle spring to open and close the contacts selectively with the consistently eflicient weldbreaking action.

Background of the invention This invention relates generally to snap acting switches and more particularly to thermally responsive, low energy, bimetallic actuated switch assemblies.

Temperature responsive, low energy switches are commonly employed for such applications as controlling air conditioning and refrigeration apparatus, a common form of such switches incorporating a bimetallic member as the temperature responsive element. It is desirable that these switches include low force and temperature differential characteristics, for example, generally below an operating force of 80 grams and below a F. temperature diiferential. The switch contacts should be actuated periodically into the open position at a lower predetermined temperature by a relatively low force to de-energize the apparatus controlled thereby, and moved into the closed position at an upper predetermined temperature, thereby again energizing the controlled apparatus. In an attempt to provide the desired low temperature differential, such a temperature responsive switch conventionally includes a snap-acting switch mechanism; however, it is extremely difiicult to furnish such characteristics and at the same time achieve any economy and sturdiness in the switch structure. It is also a problem, with low forces, to effect a consistently efficient weldbreaking motion as the contacts separate. It is further desired to provide means for readily calibrating the switch, for selectively adjusting the temperature at which the switch contacts will be closed, and the temperature differential. It is further desirable that such a switch assembly which operates with the low force and temperature differential characteristics also incorporates a simple and eflicient construction which minimizes friction, avoids loosening of the component parts, and improves the accuracy of the controls.

It is accordinglyan object of the invention to provide an improved generally low force and temperature differential snap acting switch assembly.

Another object of the invention is to provide an improved yet economical thermally responsive switch assembly having a flexible actuator.

A further object of the invention is to provide an improved yet inexpensive thermally responsive bimetallic actuated snap-acting switch assembly with low force and temperature differential characteristics and consistently good weld-breaking action as the contacts of th switch assembly are actuated to the open position.

Summary of the invention The invention in one form provides a supporting member mounting a stationary contact and a blade element formed of relatively thin flexible metal having a first section secured to the member. A second section carries a movable contact selectively between closed and open positions. A snap-producing spring means acts on the element next to the second section. A thermally responsive device, for instance a bimetallic member, applies a force to the blade element, through an actuator in engagement between the device and the element in the vicinity of the spring means in the direction of the open position as the movable contact moves from the closed to the open position. This force decreases at a rate lower than that needed to maintain the movable contact in motion to produce an accelerating action for the contact during such travel. As the contacts begin to separate from the closed position, .an angular movement is also provided to the movable contact, the forces and movement effecting a weld-breaking action to provide a consistently eflicient separation. Thus, the thermally responsive device, which is sensitive to temperature, changes the magnitude of forces acting on the actuator in response to the temperature for actuating the switch assembly. In addition, means are furnished for adjusting the ends of the bimetallic member to provide for calibration and for manual adjustment of the operating temperature.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of the preferred embodiment of the invention taken in conjunction with the accompanying drawings.

Brief description of the drawings In the drawings:

FIGURE 1 is a side cross-sectioinal view showing a thermostat for controlling air conditioning and refrigeration apparatus and incorporating the preferred form of the invention;

FIGURE 2 is an end view of the thermostat of FIG- URE 1 taken generally along the line 22;

FIGURE 3 is a top cross-sectional view taken generally along the line 33 of FIGURE 1;

FIGURE 4 is a top cross-sectional view taken generally along the line 4-4 of FIGURE 1;

FIGURE 5 is a top cross-sectional view taken generally along the line 5-5 of FIGURE 1',

FIGURE 6 is a top cross-sectional view taken generally along the line 6-6 of FIGURE 1;

FIGURE 7 is a transverse cross-sectional view taken generally along the line 77 of FIGURE 1;

FIGURE 8 is an enlarged partial view of the pivotal connection between the toggle spring and switch blade seen in FIGURE 1; and

FIGURE 9 is a representative curve showing actuating force applied to the switch blade vs. downward movement of the actuator to reveal more clearly the type of low forces and weld-breaking characteristics which may be incorporated into the type of unit illustrated in FIG- URE 1.

Description of the preferred embodiment Referring now to the figures of the drawings, the improved temperature regulating device of the invention,

generally indicated at 10 in FIGURE 1, comprises a housing member 11, which may be formed of suitable molded insulating material, having a cavity 12 formed therein. A switch blade element 13 formed of suitable relatively thin flexible metal, such as Phosphor bronze, is provided in the cavity 12. Blade element 13 has opposite end sections 14, 15, and a pair of transversely spaced apart, longitudinally extending side arm sections 16, 17, respectively, integrally joined to the end sections 14, 15 and extending therebetween. In the illustrated embodiment, a cross-bar section 18 interconnects the side arm sections 16, 17 intermediate their ends. A center section 19 is integrally joined to the end section 15 and extends toward the end section 14 between the side arm sections 16, 17. An elongated spring member 20 is provided formed of suitable relatively thin spring metal having an end 22 abutting the upper surface of end section 14 and having its other end -23 connected to the center section 19 by means of a projection 24 on the end of the center section 19 which extends through a suitable slot 25 formed in the spring member 20 adjacent end 23. Spring member 20 has a toggle spring portion 26 formed therein adjacent end 23, as best seen in FIGURE 1. End 22 of the spring member 20 and the end section 14 of the blade element 13 are respectively secured to a terminal element 27 (FIGURE 6) which in turn is attached to the housing member 11 in any suitable manner, as by staking or the like. Terminal member 27 has two male quick-connect portions '29 depending therefrom and extending outwardly from the housing member 11 to form conventional plug-on or spade terminal portions.

A center recess 30 (FIGURES l and 7) in the housing member 11 communicates with the cavity 12, and the toggle portion 26 of the spring member 20 extends downwardly into the recess 30 and engages the bottom wall 32 thereof. A movable contact 33 (FIGURE 6) is carried by the free end section 15 of the blade element 13, and a cooperating stationary contact 34 is carried by a terminal member 35 (FIGURE 1) which has terminal portion 36 depending therefrom and outwardly from the housing member 11 likewise to form spade external terminals.

In the illustrated embodiment, the toggle portion 26 in engagement with the bottom wall 32 of the recess 30 normally exerts a force on the blade element 13 so as to move the end section 15 upwardly thereby normally to close the movable and stationary contacts 33, 34. It will be readily seen, however, that a downward force exerted on the crossbar 18 against the force exerted by the toggle spring portion 26 will result in movement of the free end section 15 of the switch blade element 13 downwardly thereby to open the switch contacts 33, 34. As seen in FIGURE 8, by forming the ends of section 19 which seat against toggle spring portion 26 generally perpendicular to the upper surface of section 19 for the greater part of its width, a good yet inexpensive pivot is furnished at that location. A differential adjusting screw 37 extends upwardly through housing member 11 so that its upper end 38 acts as a stop to limit the downward movement of the free end section 15, the slotted head 39 being disposed in a recess 40' in the bottom surface 42 of the housing member 11.

A frame member 43 generally indicated by the numeral is provided having a bottom wall 44 (FIGURES 1 and and upstanding side walls 45, 46, the bottom wall 44 and cover plate 44 of member 11 being secured to the upper side 47 of the housing member 11 in any suitable manner, as by suitable rivets 48, 49 having their heads 50, 52 seated in recesses 53, 54 formed in the bottom side 42 of the housing member 11. A bottom cover member 55, which may be formed of suitable sheet insulating material, covers the recesses 40, 53, 54. The cover is suitably held in place, such as by tape 55.

A push rod member 57 is provided having a lower end 58 extending downwardly through opening 59 in the bottom wall 44 of the frame 43 with a projection seated in an opening 60 (FIGURE 6) in the crossbar section 18 of the blade element 13. Push rod member or actuator 57 has a flange 62 thereon next to its upper end 63 for the bimetal member 64 to act upon it. The generally oblong cross-section of push rod 57 and associated parts permits correct orientation of the parts and simplicity of their proper assembly into the unit.

It will now be seen that downward movement of push rod member 57 which acts downwardly on the crossbar section 18 of the switch blade element 13 against the force exerted by the toggle spring portion 26 actuates the switch blade element 13 downwardly opening the contacts 33, 34. With the contacts 33, 34 closed, a given initial downward force must be applied to provide stable movement of the push rod member 57 before the contacts 33, 34 begin to separate. However, once the movable contact 33 begins to move apart from the stationary contact 34, the downward force required to be applied to the push rod 57 to keep the movable contact 33 moving decreases sharply until the free end 15 of the switch blade element 13 engages the adjusting screw 37. It will be seen that if the push rod 57 is actuated by a flexible member, for example, elongated bimetallic member 64 in the exemplification, having a low positive spring gradient such that the downward force applied on the push rod 57 decreases at a lower rate than the decreasing upward biasing force exerted by the toggle spring required to keep the movable contact 33 moving, the movable contact 33 will be submitted to a continuously accelerated movement thereby providing a snap action.

In this regard, FIGURE 9 shows a curve a representative of the relatively low force (maximum of 50 grams, well under grams) applied on the blade member by push rod 57 and the movement of the push rod. Point A on the curve denotes the position at which the contacts snap open with a positive weld-breaking action. As the push rod applies force to the blade, the engaging contact surfaces (see FIGURE 1) tend to change relative positions or a type of prying action just prior to their snapping open. Moreover, as shown by the sharp drop-off from point A of the negative spring gradient line B of the curve of the toggle spring system when operated by bimetal member 64, a creep-type opening of the contacts does not occur. Rather, a quick change in contact position is provided even though the bimetal member 64 is operated by a low temperature differential, for instance, approximately 3 degrees F as evidenced by the relatively large rate of change in force on the blade, e.g., the slope of line B and inverse of bimetal spring gradient line C. With regard to the force on the blade, push rod 57 by virtue of the temperature sensitive bimetal member 64 in the exemplification exerts a continuous bias in the direction of the open position for the contacts, Bent tab 26 may be employed (FIGURES 1 and 6) to adjust or control the desired force to operate the contacts, adjustment of the tab away from the bimetal member decreasing the force needed to obtain the snap action.

Further, when the movable contact is snapped away from the stationary contact under low force and temperature differential conditions, there is no need for the toggle spring system to travel over-center nor for the movable contact to travel any great distance away from the stationary contact. Thus, the switch may include a low gap distance between contacts when in the open position if desired, and still include the clean contact break characteristics.

The above-mentioned actuation of the push rod member 57 is furnished by member 64 which has the high expansion strip carried away from the switch elements, the member being disposed between the side walls 45, 46 (FIGURE 4). The upper end 63 (FIGURE 7) of the push rod member 57 extends upwardly through a center opening 67 in member 64 and the area of the bottom surface of the member 64 surrounding opening 67 engages and acts downwardly upon the flange portion 62. A calibration adjusting screw 68 threadingly engages an opening 69 (FIGURE 1) in the bottom wall 44 of the frame 43 and has its lower end 70 extending into a recess 71 formed in one end of the housing member 11. The head 72 of the calibration adjusting screw 68 which has a screwdriver slot therein bears downwardly on the end 65 of the bimetallic member 64. A tension locking nut 73 is provided on the calibration adjusting screw 68 engaging the bottom surface of wall 44, and the lower end 69 of the calibration screw 68, in common with the head 72 has a screwdriver slot formed therein.

A lever member 74 has trunnions 75 seated in suitable slots 76 (FIGURE 3) formed in the side walls 45, 46 of the frame 43 thereby pivotly supporting the lever member 74. Lever member 74 has a downwardly extending flange portion 77 formed at one end thereof having a slot 78 (FIGURE 2) formed therein in which projection 79 on the end 66 of the bimetallic member 64 is seated.

A cover member 80 is provided having side flange portions 82, 83 respectively engaging the side walls 45, 46 of the frame 43. Cover member 80 is attached to the side walls 45, 46 by means of suitable tabs 84 formed on the upper edges of the side walls 45, 46 which extend upwardly through suitable slots (not shown) in the cover member 80 and are then bent over to engage the upper surface of the cover member 80 as best seen in FIGURE 2.

The lever member 74 is biased downwardly to exert a downward prestressing force on pivots or trunnions 75 of lever member 74 by means of a suitable coil spring 86 (FIGURE 1) having a center section 87 engaging a tab 88 (FIGURE 3) formed from the lever 74 and having opposite ends 89 engaging the bottom surface of the cover member 80.

A temperature adjusting knob 90 is mounted on a shaft 92 which extends downwardly through an opening 93 in the cover member 80 and has a suitable cam 94 secured thereto between the side walls 45, 46. The other end 95 of the lever member 74 has a cam follower portion 96 formed thereon which cooperatively engages the cam 94. Thus, manual rotation of the temperature adjusting knob 90 and the cam 94 results in pivotal movement of the lever member 74 about trunnions 75 thereby to adjust the amount of prestressing force applied on the end 66 of the bimetallic member 64.

It will now be seen that the bimetallic member 64 is a simple beam supported at its ends and acting directly against the switch push rod member 57, a predetermined decrease in temperature resulting in downward deflection of the bimetallic member 64 thereby to depress the push rod member 57 to actuate the switch blade element 13 to open the contacts 33, 34, and a predetermined upper temperature resulting in sufficient upward deflection of the bimetallic member 64 to permit the push rod member 57 to move upwardly permitting the toggle spring portion 26 to actuate the switch blade element 13 to close the contacts 33, 34. It will be seen that adjustable supports are provided for the two ends 65, 66 of the bimetallic beam element 64, the calibrating adjusting screw 68 providing selective adjustment of the lower temperature at which the contacts 33, 34 are opened and the lever member 74 in cooperation with the manually actuated cam 94 providing adjustable support of the other end 66 of the bimetallic beam 64 thereby selectively to control the temperature at which the contacts 33, 34 open and close.

It will further be seen that the differential adjusting screw 37 controls the contact gap and provides a simple means of adjusting the switch differential. It will further be seen that with the movable contact 33 always moving in the same direction as the push rod member 57, a high weld-breaking force may be developed by providing limited over-travel of the push rod member 57 in its downward movement. It will also be seen that the combination of the control knob and shaft 90, 92, cam 94 and lever 74 provides any desired incremental function between knob and shaft rotation and the temperature setting and thus provides more accurate control than the usual screw-nut type of adjustment which can only provide a linear function between rotation and temperature setting. The combination of an annular flange 97 on the shaft 92 overlying the upper surface of the cover member and a suitable spring 98 retains the shaft 92 and cam 94 in position.

It is desirable to provide a positive mechanical manual off or contact-open position in response to rotation of the control knob and cam 94 to one extreme position. In order to provide such a positive manual off position, a relatively stiff leaf member 99 is provided having a pair of spaced parallel leg portions 100, 102 respectively having projections 103, 104 formed at their ends 105 which extend outwardly in suitable slots 106 formed in the upper edges of the side walls 45, 46 and are retained in position by the flanges 82, 83 on the cover member 80. Member 99 has an end portion 107 formed downwardly, as at 108 which overlies and is closely spaced from the upper end 63 of the push rod member 57. A portion 109 extends toward the cam 94 and has an upwardly extending flange 110 thereon. Cam 94 has an extension portion 112 which upon rotation of the cam 94 in the direction shown by the arrow 113 from the position shown in solid lines in FIGURE 3 to the position shown in dashed lines in the same figure results in depression of the element 109 and thus downward movement of portion 107 to engage the upper end 63 of the push rod member 57 thereby positively pushing the push rod member 57 downwardly to actuate the switch blade element 13 to open the contacts 33, 34. It is thus seen that a rigid linkage is provided between the control knob and shaft 92 and the switch blade element 13 which is capable of breaking any eventual contact weld which the bimetallic member 64 may have been unable to break by its temperature responsive flexing action.

It is desirable to provide for screwdriver adjustment of the off adjustment screw 68 from either the top or the bottom of the device. To accomplish this objective, a suitable opening 114 is provided in the cover member 80 through which a screwdriver may be inserted to adjust the head 72 of the screw 68, while recess 70 is provided in the housing member 11 through which a screwdriver may be inserted for adjustment of the screw 68 by means of the screwdriver slot formed in its lower end 69. The tension nut 73 enables adjustments to be made to the off adjustment screw 68 without sealing of the screw by maintaining a constant force between the bottom wall 44 of the frame 43 and the screw, the adjustment thus being maintained without provision of any other external means.

Suitable brackets 115 are secured to the cover member 80, as by welding, and have suitable threaded openings 116 therein for attaching the switch assembly 10 to the device it is to control.

The temperature range of the switch assembly 10 above-described is calibrated by means of the calibration or off adjustment screw 68. Thus, in order to calibrate the switch assembly, it is placed in a predetermined lower ambient temperature at which the contacts are desired to be opened, the temperature control knob 90 is turned to a preselected on reading, and the screw 68 is then adjusted until the contacts open at the ambient temperature to which the switch assembly is subjected. As indicated, the controls are calibrated for a desired temperature differential by adjustment of the differential adjusting screw 37. Thus, the temperature controlling knob 90 is set to the desired on temperature, and then the control is disposed in the desired on ambient temperature and finally the differential screw 37 is adjusted to change the contact gap until the contacts close.

Consequently, it will be appreciated from the foregoing that the present invention furnishes an improved yet inexpensive low energy snap-acting switch assembly or unit having generally low force and temperature differential characteristics, especially suitable for such applications as controlling air conditioning and refrigeration apparatus. Even though the unit is economical in nature, it is of sturdy construction and is effective in providing a consistently efficient weld-breaking action as its contacts are snapped to the open position in spite of its low force and temperature difierential characteristics.

While there have been described above the principles of this invention in connection with a specific embodiment, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A thermally actuated switch assembly comprising: a supporting member; a stationary contact mounted by said supporting member; a switch blade element formed of relatively thin, flexible metal and having spaced apart first and second sections; means for fixedly securing said first section to said supporting member; a movable contact carried by said second section for selective travel between open and closed positions relative to said stationary contact; spring means connected to said switch blade element intermediate said first and second sections; said spring means continuously biasing said movable contact toward said stationary contact; a movable push rod member having a section acting on said switch blade element in the vicinity of said spring means; and a thermally responsive means continuously biasing said push rod member in the direction for continuously biasing said movable contact away from said stationary contact; said thermally responsive means changing the bias exerted on said push rod member in response to a predetermined temperature change such that the net bias exerted on said switch blade element by said spring means and said push rod member is a constantly increasing force as said movable contact moves away firom said stationary contact with a snap-action.

2. The switch assembly of claim 1 wherein said thermally responsive means is a bimetallic beam member having opposite ends, said bimetallic beam member acting on said push rod member intermediate said opposite ends,

and there are first and second means for supporting respectively said opposite ends on said supporting member.

3. The switch assembly of claim 1 wherein said spring means exerts a bias on said switch blade element which continuously decreases as said movable contact travels away from said stationary contact and said thermally responsive means exerts a bias on said push rod member which continuously decreases as said movable contact moves away from said stationary contact at a lower rate than the decreasing bias rate of said spring means, whereby said movable contact moves away from said stationary contact with a continuously accelerating motion.

4. The switch assembly of claim 2 wherein said means for supporting at least one end of said bimetallic beam member includes adjustable means for selectively adjusting the temperature at which said bimetallic beam member actuates said push rod member.

5. The switch assembly of claim 2 further comprising selectively adjustable means for selectively setting the position of said second section of said blade element relative to said stationary contact when said contacts are open thereby to adjust the differential between the temperature at which said contacts are in the open position and the temperature at which said contacts are in the closed position.

6. The switch assembly of claim 2 wherein said first supporting means comprises a selectively adjustable member connected to said supporting member and selectively varying the position of said one end of said bimetallic beam member for calibrating the temperature at which said contacts are opened.

7. The switch assembly of claim 2 wherein said second supporting means comprises a lever member pivotally mounted intermediate its ends on said supporting member, one of said lever member ends acting on the other end of said bimetallic beam member for prestressing the same; spring means acting on said lever member thereby normally to pivot the same in one direction; and man ually actuated cam means acting upon the other end of said lever member against the force exerted by said spring means thereby selectively to adjust the temperature at which said contacts are closed.

. 8. A thermally actuated switch assembly comprising: a stationary contact; a switch blade element formed of flexible material having a first section fixedly secured to a support and a second section spaced from said first section; said second section carrying a movable contact selectively between closed and open positions relative to said stationary contact; spring means connected to said switch blade element spaced from said first section and continuously exerting a bias on said movable contact toward said stationary contact which decreases as said movable contact travels away from said stationary contact; a movable actuator means for acting on said switch blade element adjacent said spring means; and a thermally responsive means sensitive to predetermined temperature changes acting upon said movable actuator means for exerting a force. on said movable actuator means and said second section of said switch blade element to continuously bias said movable contact away from said stationary contact; said thermally responsive means having a force characteristic such that the force exerted on said movable actuator means as said movable contact travels away from said stationary contact decreases at a rate lower than the decreasing bias of said spring means; whereby an accelerating motion is furnished for the movable contact during the travel.

9. The thermally actuated switch assembly of claim 8 in which said thermally responsive means moves said movable actuator means in the desired direction of movement of said movable contact for moving said movable contact away from said stationary contact and said movable actuator means is provided with over-travel to move said movable contact angularly relative to said stationary contact thereby to produce a weld-breaking action as the stationary and movable contacts are separated.

References Cited UNITED STATES PATENTS 2,315,960 4/ 1943 Hottenroth. 2,585,340 2/1952 Miller 337347 3,189,704 6/ 1965 Beck.

BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner U.S. Cl. X.R. 

